4

I want to achieve 0.05C stability in closed space to fit 24 bit ADC and voltage reference. Is it a good idea to use Peltier and heater together ?

3 Answers3

11

The Peltier can be used as a heater as well, just invert the power connection. But this kind of precision is very hard to obtain, no matter how you heat or cool down. The reason is the thermal inertia of your system: switching on the Peltier if the temperature rises won't result in an immediate temperature decrease. So you'll have to model the thermal environment and use a PID regulator which takes the thermal inertia into account. To get 0.05°C precision the environment has to be extremely stable, which means very good isolation from the outer world.
It's not impossible, but anything but easy.

Temperature stability is a requirement for meaningful 24-bit ADC, but you'll also have to take care of offsets and (thermal) noise. Offset case in point: ADCs usually have low impedance input. A 5 cm trace to the input may give an error of several bits! 1 LSB in 5V is 300nV.

stevenvh
  • 145,832
  • 21
  • 457
  • 668
  • thanks to all answering. But I appreciate your point, with focus on PID, model (mechanical design having adequate model). So it all boils down to mechanics (physics) and software magic. –  Jul 12 '11 at 15:04
  • 1
    This downplays the 0.01°C resolution of a 5 euro fever thermometer. The difference between resolution and precision... – Federico Russo Jul 12 '11 at 15:45
5

First, a Peltier device is a heater. It is also a cooler. Which it is at any one time depends on the direction of the current flow.

Yes, a Peltier device would be appropriate if you think the ambient temperature could be both above and below the desired temperature.

Controlling anything to .05C is not trivial. You will need a sensor with somewhat more resolution and repeatability than that. Get your wallet out. Once you have a suitable sensor, Peltier device, and good insulation, the rest is up to the control loop. That's a whole other subject, but there is nothing special about the control loop once you have the right feedback sensor.

Olin Lathrop
  • 313,258
  • 36
  • 434
  • 925
  • 2
    Seems we agree once again. +1 for "get your wallet out". (dammit, I've been catching up on voting and reached my daily dose. You'll get it tomorrow) – stevenvh Jul 12 '11 at 14:14
2

I was thinking about similar problem, and there are few suggestions:

1) If you have small, well-isolated stabilized area, you don't need bulky peltier for that. You can desolder usual peltier array, and use just several elements for it (they usually have about 100 modules inside)

2) I personally decided to end up on heating-only on above-ambient temperature (40C) - this is much easier/cheaper and does not need much power if isolation is good enough, as this might be completely sealed system in a vacuum for example, while peltier always conduct heat as it needs to be connected to outer world.

BarsMonster
  • 3,327
  • 5
  • 46
  • 80